Chip type capacitor, method for preparing the same and anode terminal used for preparing the same

ABSTRACT

A chip type capacitor is disclosed which has improved bond strength between an anode lead wire and an anode terminal and enhanced reliability. A method for preparing the chip type capacitor and an anode terminal used in the preparation method are also disclosed. The chip type capacitor comprises: a solid electrolytic capacitor element including an element body having an anode body, a dielectric and a cathode body, and an anode lead wire partially extending from the anode body of the element body; and an anode terminal electrically connected to the anode lead wire, the anode lead wire having such a site that about 75% or more of a periphery of a section thereof in the direction substantially perpendicular to the extending direction of the anode lead wire is covered with solidified matter resulting from solidification of a melt, the anode terminal and the anode lead wire being bonded to each other by the solidified matter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chip type solid electrolyticcapacitor, a method for preparing the same, and an anode terminal usedin the preparation method.

2. Description of the Prior Art

A chip type solid electrolytic capacitor (hereinafter often referred tosimply as “chip type capacitor”) is in the form of a chip comprising, asits core, a capacitor element having an anode-dielectric-cathodestructure. More specifically, the capacitor element has a structurecomprising an anode made of a metal exhibiting valve action (valvemetal), an oxidized layer as a dielectric layer formed over the surfaceof the anode, an electrolyte layer formed on the dielectric layer, and acathode in the form of an electrically conductive layer formed on theelectrolyte layer.

In this connection, the valve metal means a metal capable of forming anoxidized layer whose thickness can be controlled by anodic oxidation.Specifically, valve metal includes niobium (Nb), aluminum (Al), tantalum(Ta), titanium (Ti), hafnium (Hf) and zirconium (Zr). Actually, however,aluminum, tantalum and niobium are mainly used.

With respect to Al, a foil is generally used as the anode, and withrespect to Ta and Nb, a porous body prepared by sintering a Ta— orNb-based powder is used as the anode.

Of those solid electrolytic capacitors, a chip type capacitor comprisinga porous sintered body as an anode is particularly adaptable tominiaturization and capable of being adapted to have a high capacity,and hence there is strong demand therefor as a part which meets needs ofminiaturization of a cellular phone, information terminal equipment orthe like.

In recent years, for further miniaturization, there has frequently beenemployed such a structure of a chip type capacitor that electrodes (ananode and a cathode) are exposed only in the bottom surface of the chiptype capacitor.

Specifically, the structure is different from a theretofore employedstructure in which each of electrodes is exposed from a side surface andled to the bottom surface by bending in that a capacitor elementincorporated therein is so disposed as to bridge the anode terminal andthe cathode terminal (so-called “face down structure”).

By employing such a structure (face down structure), furtherminiaturization of a chip type capacitor is realized, and possibility ofoccurrence of short circuits between the electrodes and other electronicparts mounted around the electrodes is reduced. As a result, packagingdensity is increased.

A chip type capacitor having such a conventional face down structure anda method for the preparation thereof are disclosed, for example, inJapanese Patent No.3084895 by Sano et al. and in Japanese UnexaminedPatent Publication No.2001-267180 by Narita et al. In this preparationmethod, an anode lead wire of a capacitor element having a capacitorbody and the anode lead wire extending from the capacitor body is restedon an anode terminal having its portion bend to form a connectingportion, and the connecting portion and the anode lead wire are weldedtogether with a laser beam.

When the anode lead wire and the connecting portion of the anodeterminal of the capacitor are bonded to each other by theabove-mentioned method relatively high bond strength can be obtainedalthough the bond is made in a narrow area corresponding to thethickness of the anode terminal.

However, the above-mentioned method does not always provide a sufficientsurface area of the bond between the anode lead wire and the anodeterminal. Further, the method does not stably provide a sufficientdiffusion layer formed including a bonded area after the welding step.For these reasons, capacitors having insufficient bond strength arelikely to be yielded.

If the bond strength is insufficient, the anode lead wire and theconnecting portion of the anode terminal which have been bonded togetherare disconnected in a step for mounting the capacitor on a substrate.This is because the mounting step is a heat applying step, and asheathing resin filled between the element body and the anode terminalis expanded by influence of the heat to exert pushing forces on theanode body of the element body and the connecting portion of the anodeterminal in such directions that the anode lead wire and the connectingportion are brought apart from each other. Such a capacitor of which theanode lead wire and the connecting portion that have been bondedtogether are disconnected is often called an “open defectiveness”capacitor and does not function as a capacitor.

Further, it is difficult to check from an appearance of a bonded areawhether a capacitor has an “open defectiveness” or not. Accordingly,presence or absence of an “open defectiveness” has influence onreliability of electronic equipment.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems relatedto the above-mentioned “open defectiveness” and to provide a chip typecapacitor having improved bond strength between the anode lead wire andthe anode terminal and enhanced reliability, and a method for preparingthe same, and an anode terminal used in the preparation method.

According to an aspect of the present invention, there is provided achip type capacitor comprising:

a solid electrolytic capacitor element including an element body havingan anode body, a dielectric and a cathode body, and an anode lead wirepartially extending from the anode body of the element body; and

an anode terminal electrically connected to the anode lead wire, saidanode lead wire having such a site that about 75% or more of a peripheryof a section thereof in the direction substantially perpendicular to theextending direction of the anode lead wire is covered with solidifiedmatter resulting from solidification of a melt, said anode terminal andsaid anode lead wire being bonded to each other by the solidifiedmatter.

The chip type capacitor having the anode lead wire and the anodeterminal which are bonded to each other in such state has an increasedsurface area of the bonded area between the anode lead wire and theanode terminal and thus has increased bond strength in the bonded area,as compared with a conventional chip type capacitor. Accordingly, thechip type capacitor according present invention is less likely to haveso-called “open defectiveness” and has enhanced reliability as a part.

According to another aspect of the present invention, there is providedan anode terminal used for preparing a chip type capacitor comprising asolid electrolytic capacitor element including an element body having ananode body, a dielectric and a cathode body, and an anode lead wirepartially extending from the anode body of the element body; said anodeterminal having a recess for resting the extending portion of the anodelead wire and at least one protrusion located beside the recess andabove the level of the top of the extending portion of the anode leadwire rested on the recess, said protrusion being melted to supply theresulting melt to the upper surface portion of the extending portion ofthe anode lead wire, said melt being allowed to solidify to electricallyconnect the anode terminal to the anode lead wire to form a bond and anelectrical connection between the anode terminal and the anode leadwire.

By employing the anode terminal having such a structure, the extendingportion of the anode terminal has such a site that about 75% or more ofa periphery of a section thereof in the direction substantiallyperpendicular to the extending direction of the anode lead wire iscovered with solidified matter resulting from solidification of the meltobtained by heating the protrusion of the anode lead wire. The chip typecapacitor having such a structure is less likely to have “opendefectiveness” and has enhanced reliability.

According to still another embodiment of the present invention, there isprovided a method for preparing a chip type capacitor comprising a solidelectrolytic capacitor element having an anode lead wire partiallyextending therefrom; said method using an anode terminal having a recessfor resting the extending portion of the anode lead wire and at leastone protrusion located beside the recess and above the level of the topof the extending portion of the anode lead wire when the extendingportion is rested thereon, said method comprising: resting the extendingportion of the anode lead wire on the recess in such a manner that theanode lead wire is substantially perpendicular to the recess of theanode terminal; melting the protrusion by a means for heating to form amelt; allowing the melt to flow down by gravity to supply the melt tothe upper surface portion of the extending portion of the anode leadwire; and allowing the melt to solidify to bond the extending portion ofthe anode lead wire and the anode terminal to each other with theresulting solidified matter.

The manner of the resting of the extending portion of the anode leadwire on the recess may otherwise be expressed. In other words, theresting of the extending portion of the anode lead wire on the recess isconducted in such a manner that a periphery of a section of the anodelead wire in the direction substantially perpendicular to the extendingdirection of the anode lead wire has a site in contact with the recess

By employing the method, the protrusion of the anode terminal heatedinto a melt by the heating means such as a laser beam, an ion beam, arcdischarge or the like is effectively supplied to gaps between the anodelead wire and the recess and the upper surface portion of the anode leadwire. Consequently, the extending portion of the anode terminal has sucha site that about 75% or more of a periphery of a section thereof in thedirection substantially perpendicular to the extending direction of theanode lead wire is covered with solidified matter resulting fromsolidification of the melt derived from the protrusion of the anode leadwire. The chip type capacitor having such a structure is less likely tohave “open defectiveness” and has enhanced reliability.

According to a further embodiment of the present invention, there isprovided a method for preparing a chip type capacitor comprising a solidelectrolytic capacitor element having an anode lead wire partiallyextending therefrom; said method using an anode terminal having a recessfor resting the extending portion of the anode lead wire and at leastone protrusion located beside the recess and above the level of the topof the extending portion of the anode lead wire when the extendingportion is rested thereon, said method comprising: resting the extendingportion of the anode lead wire on the recess in such a manner that theanode lead wire is substantially perpendicular to the recess of theanode terminal; melting the protrusion by a means for heating to form amelt; allowing the melt to flow down by gravity to supply the melt tothe upper surface portion of the extending portion of the anode leadwire while heating the upper surface portion of the anode lead wire by ameans for heating; and allowing the melt to solidify to bond theextending portion of the anode lead wire and the anode terminal to eachother with the resulting solidified matter.

By employing the method, the protrusion of the anode terminal heatedinto a melt by the heating means such as a laser beam, an ion beam, arcdischarge or the like is effectively supplied to gaps between the anodelead wire and the recess and the upper surface portion of the anode leadwire. In addition thereto, since the upper surface portion of the anodelead wire is heated, the upper surface portion, i.e., the heated area isreadily wetted with the melt derived from the protrusion of the anodeterminal, and the melt spreads well in substantially over the portionbefore it solidifies. Consequently, the extending portion of the anodeterminal has such a site that about 75% or more of a periphery of asection thereof in the direction substantially perpendicular to theextending direction of the anode lead wire is covered with solidifiedmatter resulting from solidification of the melt derived from theprotrusion of the anode lead wire. The chip type capacitor having such astructure is less likely to have “open defectiveness” and has enhancedreliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and other objects, embodiments and effectsof the present invention will be more apparent by the followingdescription with reference to the drawings in which:

FIG. 1 is a front view schematically showing a structure of anembodiment of the chip type capacitor according to the presentinvention;

FIG. 2 is a sectional side view schematically showing the structure ofthe embodiment of the chip type capacitor according to the presentinvention;

FIG. 3 is a front view schematically showing an embodiment of the anodeterminal used for preparing the chip type capacitor according to thepresent invention;

FIG. 4 is a right side view schematically showing the embodiment of theanode terminal used for preparing the chip type capacitor according tothe present invention;

FIGS. 5(a) to 5(c) are fragmentary front views schematically showingshapes of protrusions and a recess of the anode terminal used forpreparing the chip type capacitor according to the present invention,respectively;

FIG. 6 is a structural front view schematically showing state of theanode terminal according to the present invention with an anode leadwire resting thereon at the time of initiation of laser beam welding;

FIG. 7 is a structural right side view schematically showing the stateof the anode terminal according to the present invention with the anodelead wire resting thereon at the time of initiation of laser beamwelding; and

FIG. 8 is a structural right side view schematically showing a methodfor measuring bond strength between an anode terminal and than anodelead wire with respect to a semifinished product of the chip typecapacitor according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, an embodiment of the chip type capacitor according tothe present invention will be described with reference to the drawings.

FIG. 1 is a front view schematically showing a structure of theembodiment of the chip type capacitor according to the presentinvention, and FIG. 2 is a sectional side view of the structure.

The chip type capacitor 1 comprises a capacitor element 14 including anelement body 14 b having an anode body, dielectric and cathode body andan anode lead wire 14 a partially implanted in the anode body; an anodeterminal 11 electrically connected to the anode lead wire 14 a; and acathode terminal 13 electrically connected to the cathode body of theelement body 14 b. In this embodiment, the cathode body of the elementbody 14 b and the cathode terminal 13 are connected via an electricallyconductive adhesive 16, and the capacitor element 14 and portions of theanode terminal 11 and the cathode terminal 13 other than those forconnection to external parts are sealed with a sheathing resin 15.

The element body 14 b comprises an anode body made of a Ta sintered bodyprepared by sintering a Ta-based powder, a dielectric layer in the formof an oxidized Ta layer formed over the surface of the anode body, asolid electrolyte layer made of a pyrrole polymer and formed on thedielectric layer, and a cathode body made of graphite and formed on thesolid electrolyite layer, and the element body 14 b has a substantiallyrectangular parallelepipedonal shape.

As the materials for forming the element body 14 b, there may be usedother materials than those mentioned above. As the material for theanode body, there may be used niobium, aluminum or the like, besidestantalum. As the material for the solid electrolytic layer, besides apyrrole polymer, there may be used manganese dioxide, or an electricallyconductive polymer obtained by polymerizing a monomeric material such asthiophene or a derivative thereof.

The anode lead wire 14 a is in the form of a Ta wire having asubstantially cylindrical shape in this embodiment, and the anode leadwire is partially implanted in the Ta sintered body and the otherportion thereof outward extends from the Ta sintered body.

The anode terminal 11 is a piece formed by press working of a platehaving a thickness of t. The anode terminal 11 has a bottom portion 114for connection with an external substrate or the like and a connectingportion 113 standing upward by bending at an angle of approximately 90°relative to the bottom portion 114.

In this embodiment, as the material for the anode terminal, a Ni(42%)—Fealloy (so-called “42 alloy”) which is solder-plated is used. However,other materials than this may be used. For example, copper alloys suchas a Cu—Ni—Zn alloy, e.g., a German silver (45-65% Cu, 6-35% Ni, and15-35% Zn), and a phosphor bronze (e.g., 95% Cu, 5% Sn, and 0.2% P) maybe used. Further, the material for the plating may contain silver with aview to improving bonding properties.

A site of the substantially cylindrical extending portion of the anodelead wire 14 a and the connecting portion 113 of the anode terminal 11together form a junctional area 115 electrically connecting the anodeterminal 11 to the anode lead wire 14 a via solidified matter 116resulting from solidification of a melt. In this junctional area, about75% or more of a periphery of a section of the site in the directionsubstantially perpendicular to the extending portion of the anode leadwire 14 a. About 75% or more means that an about ¼ upper portion of aperiphery of the anode lead wire 14 a, which has not been covered withsolidified matter in a conventional chip type capacitor in a portion, isat.least partially covered with the solidified matter 116.

While the periphery of the section of the anode lead wire 14 a in thedirection substantially perpendicular to the extending direction of theanode lead wire is covered with the solidified matter 116, gaps betweenthe recess of the connecting portion 113 of the substantially flat anodeterminal 11 and the anode lead wire 14 a rested on the recess is filledwith the solidified matter 116. In consequence, sufficient bond strengthis obtained

The cathode terminal 13 is a piece formed by press working of ? a platemade of a Ni(42%)—Fe alloy (so-called “42 alloy”) which issolder-plated, and the cathode terminal has a bottom portion 131 and amounting portion 132 extending at a level higher than that of the bottomportion 131 and in parallel with the bottom portion 131. To the uppersurface of the mounting portion 132, the cathode body which is theperipheral layer of the capacitor element 14 is electrically connectedvia the electrically conductive adhesive 16.

By employing the above-described structure, in the chip type capacitoraccording to the present invention, bond strength between the anode leadwire 14 a and the anode terminal 11 is improved as compared with aconventional chip type capacitor. Accordingly, the chip type capacitoraccording present invention is less likely to have so-called “opendefectiveness” and has improved reliability as a part.

From the view point of reducing possibility of occurrence of “opendefectiveness”, it is preferred that about 90% or more of a periphery ofa section of the anode lead wire 14 a in the direction substantiallyperpendicular to the extending direction of the anode lead wire 14 a becovered with the solidified matter 116.

Further, from the viewpoint of improvement and stability of bondstrength, it is particular preferred that the solidified matter 116 andthe anode lead wire 14 a be and the solidified matter 116 and the anodeterminal 11 be diffusively bonded, and as a result, a diffusion layer 12be formed.

To form the solidified matter 116, a melt may be supplied by melting aportion of the anode terminal 11 or may be externally supplied and themalt is allowed to solidify.

In the case where a melt for forming the solidified matter 116 issupplied by melting a portion of the anode terminal 11, there is anadvantage that the melt is stably supplied, and further, there is amanufacturing advantage that preparation steps are simplified. In thiscase, when the material of the anode terminal is capable of easilyforming a diffusion layer in connection with the material of the anodelead wire 14 a, the solidified matter 116 is further firmly bonded tothe anode lead wire by virtue of the presence of the diffusion layer.Accordingly, in addition to the above-described advantages, there is anadvantage that a chip type capacitor which is less likely to have “opendefectiveness” is obtained.

On the other hand, in the case where a melt is externally supplied,there is an advantage that a range of selection of the material isbroad. For example, even if a material of the anode terminal 11 and amaterial of the anode lead wire 14 a are not capable of easily forming adiffusion layer in connection with each other, bond strength between theanode terminal 11 and the anode lead wire 14 a may be increased byexternally supplying a melt of a material capable of easily forming adiffusion layer in connection with the materials of the anode terminal11 and the anode lead wire 14 a. As the material capable of easilyforming a diffusion layer, there may be mentioned a material containingthe same component as in the materials of the anode terminal 11 and theanode lead wire 14 a, a material containing a component capable ofeasily diffusing into the materials of the anode terminal 11 and theanode lead wire 14 a, and a material into which a component orcomponents of materials of the anode terminal 11 and the anode lead wire14 a may easily diffuse. The component diffused in the other phase orother phases may form an alloy or a solid solution.

Subsequently, description will be given with respect to the anodeterminal 11 used for preparing the chip type capacitor according to thepresent invention with reference to FIGS. 3 to 5.

FIG. 3 is a front view schematically showing an embodiment of the anodeterminal used for preparing the chip type capacitor according to thepresent invention, and FIG. 4 is a sectional side view of the embodimentviewed from the right.

The anode terminal 11 is a piece formed by press working of a platehaving a thickness of t. The anode terminal 11 has a bottom portion 114for connection with an external substrate or the like and a connectingportion 113 standing upward by bending at an angle of approximately 90°relative to the bottom portion 114.

In this embodiment, as the material for the anode terminal, a Ni(42%)—Fealloy (so-called “42 alloy”) which is solder-plated is used. However,other materials than this may be used. For example, copper alloys suchas a Cu—Ni—Zn alloy, e.g., a German silver (45-65% Cu, 6-35% Ni, and15-35% Zn), and a phosphor bronze (e.g., 95% Cu, 5% Sn, and 0.2% P) maybe used. Further, the material for the plating may contain silver with aview to improving bonding properties.

The connecting portion 113 is provided with a pair of substantially flatprotrusions 111 and 112 and, therebetween, a recess 113E for resting theanode lead wire 14 a thereon. These protrusions are provided forstabilizing the resting of the anode lead wire 14 a on the recess and asa source for supplying the melt to weld the connecting portion 113 andthe anode lead wire 14 a together.

In this embodiment, the anode terminal 11 is a piece formed by pressworking of a plate having a thickness of t. Accordingly, the protrusions111 and 112 are substantially flat. However, each of the protrusions maynot be flat and may have any shape so long as a melt derived therefromis efficiently supplied to the upper surface portion of the anode leadwire 14 a rested on the recess 113 in the subsequent step of melting.

The configuration of the connecting portion 113 of the anode terminal 11according to the present invention will be described in more detail withreference to FIGS. 5(a) to 5(c). FIGS. 5(a) to 5(c) are fragmentaryfront views schematically showing shapes of the protrusions and therecess of the anode terminal used for preparing the chip type capacitoraccording to the present invention, respectively.

Now, explanation will be given with respect to several terms used in thefollowing description. “Anode lead wire level Lv14 a” means the level ofthe top of the anode lead wire 14 a with the anode lead wire 14 a restedon the recess 113E of the connecting portion 113. In other words, theanode lead wire level Lv14 a means the level above the bottom of theU-shape of the recess 113E shown in FIG. 5(c) by the diameter of theanode lead wire 14 a.

“Lower part 113B of the connecting portion” means the part of theconnecting portion below the anode lead wire level [Lv14 a shown inFIGS. 5(a) and 5(b)]. “The protrusions 111, 112” mean the parts of theconnecting portion above the anode lead wire level.

“Heights H1, H2 of the protrusions”:

The shape of the protrusion 111 which is used as a material for coveringthe upper surface portion of the anode lead wire in this embodiment isshown in FIG. 5(a).

The protrusion 111 is provided for covering the upper surface portion ofthe anode lead wire by melting the protrusion itself and is so formed asto protrude from the anode lead wire level Lv14 a by its height H1.

The anode terminal 11 according to the present invention has itsprotrusion 111 melted, for example, by a laser beam to weld theconnecting portion 113 and the anode lead wire 14 a together, asdescribed below. Accordingly, the height H1 of the protrusion 111 is ina range which is determined based on the focal length of the laser beamthat is used to melt the protrusion 111 itself and on the volume of theprotrusion 111. Specifically, the range is determined taking intoconsideration the following formula (1) showing relationship amongwidths W1, W2 (described below) of the protrusion 111 and the thicknesst of the plate, and factor of safety α (>1) of the covering of the uppersurface portion of the anode lead wire and volume V of the covering.(W 1+W 2)×H 1×t×½=V×α  (1)

The height H1 of the protrusion 111 is preferably in such a range that asufficient efficiency of the melting is maintained during the periodfrom initiation to termination of the melting of the protrusion 111without changing the vertical position of the laser beam source emittingthe laser beam, i.e., the focal length of the laser beam.

In a case where only one protrusion 111 is used as the material memberfor covering the upper surface portion of the anode lead wire 14 a, onlyone position may be heated and the step of melting is thereby thestructure of the heating means for melting is simplified. An example ofthe shape of the other protrusion 112 in the case where only theprotrusion 111 is melted is shown in FIG. 5(b).

In the case where only one protrusion 111 is used as the source of themelt, the other protrusion may not necessarily be formed. However, it ispreferred that the other protrusion 112 be formed. In other words, theother protrusion 112 is preferably so formed as to have such a height H2that the top of the protrusion 112 is at a level higher than the anodelead wire level 14 a even slightly, thereby obtaining an effect ofpreventing the melt of the protrusion from flowing down from the uppersurface portion of the anode lead wire.

“Widths W1, W2 of the protrusion”:

The widths W1 and W2 which specify the shape of the protrusion aredefined as follows.

The protrusion 111 has such a shape that its width is graduallyincreased from the width W1 toward the end surface 111 c.

The width W1 is a width of the protrusion 111, which is used forcovering the upper surface portion of the anode lead wire, at a level P1of the center C of the anode lead wire as shown in FIG. 5(a).

The width W2 is, in substance, a width of the end surface 111 c of theprotrusion 111 and is determined taking into consideration extent ofheat transfer with the laser beam with which the protrusion isirradiated and the volume of the protrusion.

Incidentally, the end of the end surface 111 c may be beveled from theviewpoint of improvement in manageability, as shown in FIG. 5(a).

Further, in FIG. 5(a), the anode terminal 11 has such a shape that itsleft side portion relative to the recess is increased in width from aposition above the level P1 toward the top of the anode terminal.However, the width may be increased from a position at the level P1 orbelow the level P1 toward the top of the anode terminal.

“Shape of the lower part of the connecting portion between theprotrusions 111, 112”:

The lower part 113B of the connecting portion is a part below the anodelead wire level Lv14 a. In other words, the lower part of the connectingportion consists of parts below the protrusions 111, 112 and a parttherebetween. The lower part 113B of the connecting portion is providedwith a recess 113E which conforms to the lower half of thecross-sectional contour of the anode lead wire. In FIG. 5(c), a case isshown where the cross-sectional shape of the anode lead wire iscircular. By employing such a configuration, the lower half of theperiphery of the anode lead wire is in linear or ribbon-wise contactwith the edge of the recess 113E when the anode lead wire is rested onthe recess. Accordingly, diffusion bonding by the welding is efficientlyeffected to thereby obtain a chip type capacitor which is less likely toundergo open deficiency.

Width W3 of gap between the protrusions:

The width W3 is the maximum width of the recess 113E of the connectingportion. When the cross-sectional shape of the anode lead wire iscircular, the width W3 is the width of the recess 113E at a levelincluding the center C of the anode lead wire rested on the recess 113E,as shown in FIG. 5(c).

The width W3 preferably includes such an allowance that clearance ofabout 2 μm to about 50 μm, more preferably about 5 μm to about 20 μm isleft between the anode lead wire and the anode terminal when the anodelead wire is rested on the recess 113E of the connecting portion. Inother words, the width W3 is preferably about 2 μm to about 50 μm, morepreferably about 5 μm to about 20 μm larger than the width of the anodelead wire at the same level. In the case of FIG. 5(c), the width W3 ispreferably about 2 μm to about 50 μm, more preferably about 5 μm toabout 20 μm larger than the diameter of the anode lead wire. If theclearance is larger than about 50 μm, the anode lead wire is likely torest unstably on the recess, or melt 111L of the protrusion 111 can besupplied to the clearance between the anode lead wire and the recess113E of the connecting portion in an amount insufficient for filling theclearance with the melt. Accordingly, it is difficult to stably obtainsufficient bond strength. On the other hand, if the clearance is smallerthan 2 μm, it can be difficult to rest the anode lead wire on the recess113E, or the melt 111L of the protrusion 111 cannot penetrate into theclearance between the anode lead wire and the recess 113E of theconnecting portion. Accordingly, in this case also, it is difficult tostably obtain sufficient bond strength.

Positional relationship between the protrusions 111, 112 and the anodelead wire 14 a:

The protrusion 111 is located above the level of the anode lead wire 14a, and the anode lead wire 14 a is disposed adjacent thereto. Further,the width direction of the end surface 111 c at the top of theprotrusion 111, i.e., the thickness direction of the protrusion 111 andthe longitudinal direction of the anode lead wire 14 a are orthogonal toeach other.

By this arrangement, when the protrusion 111 is melted in the laser beamwelding, the melt 111L flows down by gravity to cover the upper surfaceportion of the anode lead wire 14 a. In this connection, the directionin which the melt 111L flows down can be controlled by changing theposition at which the protrusion is irradiated with a ? laser beam orintensity of the irradiation.

The protrusion 111 preferably has its side end surface 111 a whichextends tangentially relative to the anode lead wire 14 a formed in alinear shape geometry extending in the vertical direction so that theupper surface portion of the anode lead wire 14 a is efficiently coveredwith the melt 111L of the protrusion 111 which flows down by gravity inthe laser beam welding.

Further, when the protrusion 111 is melted using a laser beam, theprotrusion 111 is irradiated with the laser beam from above.Accordingly, also from the viewpoint that the protrusion 111 does notintercept the laser beam from the anode lead wire 14 a, the tangentialside end surface 111 a is formed preferably in a linear shape geometryextending in the vertical direction.

As the source of the melt for covering the upper surface portion of theanode lead wire therewith, both the protrusions 111, 112 may be used. Inthis case, shapes and sizes of the protrusions are so determined as toenable the volume of the melt derived from the protrusions to cover theupper surface portion of the anode lead wire.

In this embodiment, the protrusion 111 is melted with a laser beam.Besides a laser beam, however, an electron beam, an ion beam or arcdischarge may be employed to melt the protrusion.

Subsequently, the method for preparing a chip type capacitor which usesthe above-described anode terminal 11 will be described.

Method for preparing a chip type capacitor

Steps of the preparation of the chip type capacitor will be describedwith reference to FIGS. 1 and 2.

Preparation of capacitor element 14 (Step 11: S11)

(i) A Ta-based powder is prepared, and an anode lead wire 14 a ispartially inserted in the Ta-based powder. The Ta-based powder with theanode lead wire partially inserted therein is pressed into a rectangularparallelepipedonal shape and then sintered under vacuum to form a Taporous body.

(ii) An oxidized Ta layer is formed as a dielectric layer over thesurface of the Ta porous body by anodic oxidation.

(iii) On the oxidized Ta layer formed over the surface of Ta porousbody, a solid electrolyte layer and a graphite layer and a silver(Ag)paste layer are sequentially formed.

Preparation of anode terminal 11 and cathode terminal 13 (Step 12: S12)

A band plate (lead frame material) made of a solder-plated 42 nickelalloy is subjected to continuous press working to prepare anodeterminals 11 and cathode terminals 13. In the press working, punchingand bending are performed as follows.

(i) Punching:

Contours of anode terminals 11 and cathode terminals are formedcontinuously by punching in such an arrangement that a pair of an anodeterminal 11 and a cathode terminal 13 which will be incorporated in thesame capacitor are in the width direction of the lead frame and that aplurality of pairs of an anode terminal 11 and a cathode terminal 13 arein the longitudinal direction of the lead frame (progressive punchingpress). At this stage, a bottom portion 114 and a connecting portion 113of each of the anode terminals 11 and a bottom portion 131 and amounting portion 132 of each of the cathode terminals 13 are coplanarwith each other on the same plane, and each of the bottom portions 114,131 are unseparated form the lead frame.

The contour of the anode terminal 11 is as described above, and thecontour of the cathode terminal 13 is basically such a simplerectangular shape that the bottom portion 131 and the mounting portion132 stretch in a line.

(ii) Bending:

In the cathode terminal 13, the bending is so effected as to form a stepbetween the bottom portion 131 and the connecting portion 132.

In the anode terminal 11, the connecting portion 113 is bent in anangler amount of approximately 90° relative to the bottom portion 114.

Connecting the cathode terminal 13 to the capacitor element 14 (Step 13:S13)

An electrically conductive adhesive 16 is applied onto the mountingportion 132 of the cathode terminal 13, and the capacitor element 14 isplaced thereon to electrically connect the cathode terminal 13 to theperipheral layer, i.e., the cathode of the capacitor element 14 via theelectrically conductive adhesive 16.

Bonding of anode terminal to the capacitor element by laser beam weldingwhich is to be subsequently performed will be described with referenceto FIGS. 6 and 7.

FIG. 6 is a structural front view schematically showing state of theanode terminal according to the present invention with an anode leadwire resting thereon at the time of initiation of the laser beamwelding, and FIG. 7 is a structural right side view schematicallyshowing the same.

In the preparation method according to the present invention, (a)position of irradiation, (b) focal length and depth of focus, (c) laserpower, (d) pulse, and (e) irradiation time may be mentioned asconditions of the laser beam welding. Of these conditions, (a) positionof irradiation is particularly important. Accordingly, position ofirradiation will be described in detail.

(a) position of irradiation

i) irradiation of the protrusion

Referring to FIG. 6, the protrusion 111 is irradiated with a laser beamL18 from laser irradiation equipment 18 at a position P2 in the top endsurface 111 c which point is nearer to the recess-proximal end than therecess-distal end of the top end surface 111 c.

It is preferred that the position P2 be slightly apart from therecess-proximal end of the top end surface 111 c. Specifically, theposition P2 is apart from the recess-proximal end of the top end surface111 c by preferably about 2% to about 50%, more preferably about 3% toabout 10% of the width W2 of the top end surface 111 c. By irradiatingthe protrusion 111 at a position in the above-mentioned range, the melt111L of the protrusion is efficiently supplied to the upper surfaceportion of the anode lead wire 14 a. Referring to FIG. 7, in thethickness direction of the protrusion 111, the protrusion is irradiatedpreferably at the center of the thickness thereof.

By the irradiation with the laser beam at the position P2, a portion ofthe protrusion 111 around the position P2 is heated to melt. FIG. 6shows the state at the initial stage of the melting. A portion of theprotrusion within the area of which border is equidistant from theposition P2 of irradiation is heated into a melt 111L as a liquid phase,and the interface IF1 between the melt as a liquid phase and the otherportion as a solid phase of the protrusion makes a characteristicallycurved slope from the top of the protrusion 111 toward the anode leadwire 14 a. Accordingly, the melt 111L flows down toward the anode leadwire 14 a to cover the upper surface portion of the anode lead wire.While covering the upper surface portion of the anode lead wire, themelt cools and solidifies.

By continuing the irradiation of the protrusion 111 with the laser beamL18, the melted area is further expanded, and the resulting melt 111Lflows down to the anode lead wire 14 a. The “melting—flowing down” iscontinuously advanced. Finally, the protrusion 111 is meltedsubstantially in whole, and the resulting melt flows down toward theanode lead wire 14 a to cover the upper surface portion of the anodelead wire.

ii) Irradiation of the anode lead wire 14 a

The anode lead wire 14 a as well as the protrusion 111 is irradiatedwith the laser beam L18 from the laser irradiation equipment 18 to heata portion of the anode lead wire 14 a. The area of the anode lead wirewhich is subjected to the irradiation with the laser beam thereby has anelevated temperature, and the surface of the anode lead wire in the areais activated and improved in wettability with the melt 111L, Inconsequence, the melt 111L efficiently cover the upper surface portionof the anode lead wire 14 a.

In the heating, the temperature for heating the surface of the anodelead wire 14 a is preferably the melting point of the protrusion 111(,i.e., the solidifying point of the melt 111L) or higher and lower thanthe melting point of the anode lead wire 14 a.

To improve the wettability of the anode lead wire 14 a with the melt111L, a higher heating temperature yields a better result. However, ifthe anode lead wire 14 a is considerably melted, it can be adverselyaffected to ensure a satisfactory electrical connection between thecapacitor element and the anode terminal. Accordingly, the heatingtemperature is preferably lower than the melting point of the anode leadwire 14 a. Specifically, when the anode terminal 11 is made of a 42alloy, the heating temperature is preferably in a range of about 1,400°C. or higher and lower than about 3,000° C. with respect to a Ta anodelead wire and in a range of about 1,400° C. or higher and lower thanabout 2,500° C. with respect to an Nb anode lead wire.

The anode lead wire 14 a and the protrusion 111 may be irradiated with alaser beam L18 from a single laser beam source.

In such a case, the irradiation may be carried out with a laser beam L18having an enlarged light flux which allows the anode lead wire 14 a andthe protrusion 111 to be targeted in the vicinity of the laser beam.

According to this method, the heating for melting the protrusion 111 andthe heating for improving wettability of the anode lead wire 14 a may beconducted without using a complicated optical system. Further,efficiency of use of laser energy is improved. In this method also, theprotrusion 111 is irradiated with the laser beam L18 at a position apartfrom the recess-proximal end of the top end surface 111 c by preferablyabout 2% to about 50%, more preferably about 3% to about 10% of thewidth W2 of the top end surface 111 c.

Further, irradiation may be conducted by scanning the laser beam L18between the irradiation point P2 of the protrusion 111 and a target areaon the anode lead wire 14 a, i.e., by alternately irradiating theprotrusion 111 at the irradiation point P2 and the target area on theanode lead wire 14 a.

Alternatively, a laser beam from a single laser beam source may be splitto irradiate the protrusion 111 at the irradiation point P2 and thetarget area on the anode lead wire 14 a with split laser beams.

(b-e) Other conditions

With respect to a depth of focus, with a view to reducing energyvariation over a period of the laser beam welding step, an opticalsystem is preferably so set as to emit a laser beam L18 with a largedepth of focus. For example, numerical aperture (NA) of a lens may bereduced to thereby obtain a large depth of focus so long as anyundesirable effect is not caused. A focal length, laser power, pulse,and a irradiation time are determined taking into consideration theshape and the material of the protrusion 111. Specifically, theseconditions are preferably so determined that the protrusion 111 isirradiated into a melt 111L stably without bumping and the melt 111L issupplied to the upper surface portion of the anode lead wire 14 a. ?

When both of the protrusions 111 and 112 are used as sources of a meltfor covering the upper surface portion of the anode lead wire 14 a, alaser beam L18 is applied to each of the protrusions.

The state of the bond between the anode lead wire 14 a and theconnecting portion 113 when the above-described laser beam welding stephas finished is schematically shown in FIG. 1.

As shown in FIG. 1, the protrusion 111 has already been melted by thelaser beam welding to cover the upper portion of the anode lead wirewith the resulting melt. As a result, 75% or more of a periphery of asection of the anode lead wire 14 a in the direction substantiallyperpendicular to the direction in which the anode lead wire extends fromthe capacitor body 14 b is covered with solidified matter 116.

Further, owing to the heat of solidification of the melt 111L and theheating of the anode lead wire 14 a with the laser beam L18, diffusionproceeds between the anode lead wire 14 a and the solidified matter 116and between the anode lead wire 14 a and the connecting portion 113 toform a diffusion layer 112 in an area where the anode lead wire 14 a iscovered. By virtue of the formation of the diffusion layer 12, thejunctional area 115 where the anode lead wire 14 a and the connectingportion 113 are bonded to each other has extremely high bond strength.When the anode lead wire 14 a is made of Ta and the anode terminal 11 ismade of a solder-plated Ni(42%)—Fe alloy plate, the diffusion layer 12contains Ta, Ni, Fe and Sn as main components.

After the above-described laser beam welding, a chip type capacitor asshown in FIG. 2 is completed through conventional subsequent preparationsteps.

The chip type capacitor prepared by the above-described preparationmethod has a larger junctional area 115 and higher bond strength of thejunctional area 115 as compared with a conventional chip type capacitor.Accordingly, the chip type capacitor according to the present inventionis less likely to have so-called “open defectiveness” and highlyreliable as a part.

EXAMPLES

The following Examples are given by way only of illustrations for moreclear understanding of the present invention. It is, therefore, to beunderstood that the scope of the present invention is by no meansrestricted to these specific Examples.

Example 1

Through the following procedure, a chip type capacitor which was not yetsubjected to a step of sheathing by molding (a semifinished chip typecapacitor) was prepared.

Using conventional technique, a capacitor element having a Ta anode bodywas prepared which had a rectangular paralellepipedonal shape of 1.6 mmin length, 0.85 mm in width and 0.8 mm in height and which is providedwith a Ta anode lead wire having a diameter of 0.15 mm.

On the other hand, an anode terminal having a shape as shown in FIGS. 3to 5 and a cathode terminal having a shape as shown in FIG. 2 wereprepared. Each of them was made of a nickel(42%)-iron alloy plate(solder-plated). Specific dimensions with respect to the protrusion ofthe anode terminal were as follows. (i) width W1:  0.1 mm (ii) heightH1: 0.24 mm (iii) width W2:  0.3 mm (iv) width W3: 0.15 mm (+ allowanceof 0.01 mm) (v) thickness t of the plate: 0.08 mm

Then, the Ta capacitor element and the cathode terminal were bondedtogether with an electrically conductive adhesive, and the anode leadwire of the Ta capacitor element was rested on a recess of a connectingportion of the anode terminal. The maximum width of clearance betweenthe anode lead wire and the recess of the connecting portion after theanode lead wire was rested on the recess was 0.01 mm (10 μm) as theabove-mentioned allowance was provided.

Subsequently, the top end surface of the protrusion and the uppersurface portion of the anode lead wire were irradiated with about 0.3Jof a laser beam having a radius of light flux of 0.3 mm at the focalpoint so as to concurrently irradiate two of them with the laser beam.The center position at which the top end surface of the protrusion wasirradiated was a position 0.015 mm apart from the recess-proximal end ofthe top end surface, and it was the center of the top end surface in thethickness direction of the protrusion. The temperatures of the heatingby the irradiation with the laser beam were about 1,500° C. and about1,800° C. with respect to the protrusion and the anode lead wire,respectively. The temperature at the protrusion was lower than that atthe anode lead wire because of the heat of fusion at the protrusion.

As a result, the protrusion of the anode terminal was melted by theirradiation with the laser beam, and the resulting melt was allowed toflow toward the anode lead wire to substantially cover the anode leadwire therewith and then solidified.

Of the semifinished chip type capacitors obtained by the above-describedpreparation method, 20% were evaluated to be defective on the groundsthat the melt had not been supplied to the intended position.

With respect to the semifinished chip type capacitors evaluated to benon-defective, average percentage of covering the periphery of thesection of the anode lead wire in the direction substantiallyperpendicular to the extending direction of the anode lead wire with thesolidified matter resulting from the solidification of the melt of theprotrusion of the anode terminal was about 95%.

Example 2

Each of semifinished chip type capacitors were prepared in the samemanner as in Example 1 except that a top end surface of a protrusion andan anode lead wire were irradiated with a laser beam by scanning thelaser beam.

In any of the thus obtained 33 semifinished chip type capacitors, a meltwas supplied to the intended place.

With respect to the semifinished chip type capacitors, averagepercentage of covering the periphery of the section of the anode leadwire in the direction substantially perpendicular to the extendingdirection of the anode lead wire with the solidified matter resultingfrom the solidification of the melt of the protrusion of the anodeterminal was about 95%.

Comparative Example 1

Anode terminals were prepared which had the same shape as of the anodeterminal used in Example 1 except that H1 was 0 mm and W2 was 0.1 mm andH2 was 0 mm.

Using an anode terminal of this type, each of semifinished chip typecapacitors was prepared in the same manner as in Example 1 except thateach of the portions on the both sides of the recess was irradiated withabout 0.3J of a laser beam at a target position 0.015 mm apart from therecess-proximal end of the top end surface thereof.

Of the 40 semifinished chip type capacitors prepared by theabove-described method, 7 capacitors (about 20%) were evaluated to bedefective on the grounds that a melt had not been supplied to theintended position.

With respect to the semifinished chip type capacitors evaluated to benon-defective, average percentage of covering the periphery of thesection of the anode lead wire in the direction substantiallyperpendicular to the extending direction of the anode lead wire with thesolidified matter resulting from solidification of the melt of theprotrusion of the anode terminal was about 65%.

Measurement of bond strength

Of the semifinished products prepared in Examples 1 and 2 andComparative Example 1, bond strength between the capacitor element andthe anode lead wire-was measured with respect to each of thesemifinished products evaluated to be non-defective. A method for themeasurement will be described with reference to FIG. 8. FIG. 8 is astructural right side view schematically showing a method for measuringbond strength between the anode terminal and the anode lead wire withrespect to the semifinished product of the chip type capacitor accordingto the present invention.

First, the capacitor element 14 and the cathode terminal 13 were fixedto each other by a fixing means 52 provided therebetween, and thecapacitor element 14 and the bottom portion 114 of the anode terminal 11are fixed to each other by a fixing means provided therebetween. Bondstrengths by the fixing means 52, 53 were set to be sufficiently greaterthan the bond strength between the capacitor element 14 and anodeterminal 11.

Subsequently, the anode lead wire 14 a was held by a wire 511, and thewire was connected to a measuring device 51. The measuring device 51 waspulled upward until the bond between the capacitor element 14 and theanode terminal 11 was broken. The force at the time of the breakage wasdetermined as the bond strength.

With respect to each of Examples 1 and 2 and Comparative Example 1, bondstrengths of 33 semifinished products were measured.

As a result, the bond strengths were 2.5N on average with respect toeach of Examples 1 and 2 and 1.9N on average with respect to ComparativeExample 1.

1-9. (canceled)
 10. A method for preparing a chip type capacitorcomprising a solid electrolytic capacitor element having an anode leadwire partially extending therefrom; said method using an anode terminalhaving a recess for resting the extending portion of the anode lead wireand at least one protrusion located beside the recess and above thelevel of the top of the extending portion of the anode lead wire whenthe extending portion is rested thereon, said method comprising: restingthe extending portion of the anode lead wire on the recess in such amanner that the anode lead wire is substantially perpendicular to therecess of the anode terminal; melting the protrusion by a means forheating to form a melt; allowing the melt to flow down by gravity tosupply the melt to the upper surface portion of the extending portion ofthe anode lead wire; and allowing the melt to solidify to bond theextending portion of the anode lead wire and the anode terminal to eachother with the resulting solidified matter.
 11. The method for preparinga chip type capacitor according to claim 10, wherein the position in thetop end surface of the protrusion at which the protrusion is melted byheating is a position apart from the recess-proximal end of the top endsurface by about 2% to about 50% of the width of the top end surface inthe direction substantially perpendicular to the extending direction ofthe anode lead wire.
 12. The method for preparing a chip type capacitoraccording to claim 10, wherein the melt is supplied to the upper surfaceportion of the anode lead wire while heating the upper surface portionof the anode lead wire by a means for heating.
 13. The method forpreparing a chip type capacitor according to claim 12, wherein the meansfor heating the upper surface portion of the anode lead wire is the sameheating means as for melting the protrusion.
 14. The method forpreparing a chip type capacitor according to claim 12, wherein thetemperature for heating the upper surface portion of the anode lead wireis the solidifying point of the material of the melt or higher and lowerthan the melting point of the material of the anode lead wire.
 15. Themethod for preparing a chip type capacitor according to claim 10,wherein the means for heating is irradiation with a laser beam.
 16. Themethod for preparing a chip type capacitor according to claim 13,wherein the means for heating the protrusion and the upper surfaceportion of the anode lead wire is irradiation with a laser beam.
 17. Themethod for preparing a chip type capacitor according to claim 16,wherein the protrusion and the upper surface potion of the anode leadwire are irradiated with a laser beam by scanning the laser beam. 18-19.(canceled)